A wide assortment of implantable medical devices are presently known and in commercial use. Such devices include cardiac pacemakers, cardiac defibrillators, cardioverters, neurostimulators, and other devices for delivering and/or receiving electrical signals to/from a portion of the body. Sensing and/or stimulating leads extend from the associated implantable medical device to a distal tip electrode or electrodes in contact with body tissue. These electrodes should be securely fixed to the tissue to facilitate electrical stimulation or sensing by the implantable medical device.
In order to work reliably, leads need to be stably located adjacent to the tissue to be stimulated or monitored. One common mechanism for accomplishing this has been the use of a fixation helix, which exits the distal end of the lead and is screwed directly into the body tissue. The helix itself may serve as an electrode or it may serve as an anchoring mechanism to fix the position of an electrode mounted to or forming a portion of the lead itself. This is known in the art as active fixation. The fixation helix electrode and lead must be resistant, during and after implantation, to damage both through torsion and tension. The reason they must be resistant to torsion is that during the initial implant, the physician applies a torque tool to the proximal end, which he then twists in order to drive the helix screw into body tissue. If the physician does not achieve a desired capture level or desired pacing site, the physician may unscrew the helix and then pull on the lead to re-position it at a different site. This pull force creates a tension on the lead and its associated distal tip electrode components. Another reason that tensile force may be applied to the lead is during lead extraction surgeries. Generally, lead extraction surgery is done to replace a damaged lead or one that has poor insulation resistance.
One problem associated with implanted leads is that they act as an antenna and tend to pick up stray electromagnetic signals from the surrounding environment. This is particularly problematic in an MRI environment where the currents which are imposed on the leads can cause the leads to heat to the point where tissue damage is likely. Moreover, the currents developed in the leads during an MRI procedure can damage the sensitive electronics within the implantable medical device. Bandstop filters, such as those described in U.S. Pat. No. 7,363,090 and U.S. 2007/0112398 A1, which are herein incorporated by reference, reduce or eliminate the transmission of damaging frequencies along the leads while allowing the desired biological frequencies and pacing pulses to pass efficiently through. However, when implanting the medical electrical lead, stress can be applied directly to the bandstop filter or electrical components either through torsion or tensile loads. Such loads are created because the electrical components are mechanically connected to the lead, and may damage the electrical components during the implanting procedure. This is obviously a negative occurrence which should be avoided.
Accordingly, there is a need for an implantable medical lead having an electronic component such as a low pass filter or bandstop filter, wherein the torsional and tensile loads applied to the electronic component during implantation are reduced or even eliminated. The present invention fulfills these needs and provides other benefits.